A burn pit left smoldering overnight at the edge of the woods was the cause of the destructive 2015 Sockeye fire, investigators testified Thursday in the trial of a couple accused of starting the fire.

Fire Investigator Ethan Eley testified to the Palmer jury about how he and fellow Division of Forestry Investigator Tom Greiling came to the conclusion the Sockeye fire had begun on the Willow property of Greg Imig.

Imig, 61, and his wife, Amy DeWitt, 43, are each charged with a dozen counts related to starting the blaze, including second-degree negligent burning, failure to obtain a burn permit, burning without clearing the area, allowing the wildfire to spread and leaving the fire unattended.

Eley told jurors about his arrival at the property the night the fire started on June 14. He arrived there after aerial surveys from firefighters and first responders indicated the fire had originated near the property. Eley stayed there overnight, not sleeping, listening to his radio and securing the property.

He and fellow investigator Greiling began to survey the area the next morning. It was then that Greiling noticed boards on the edge of the property near the spruce forest.

"It just looked strange to him and it did appear strange to me too, but I hadn't had time to look at it specifically," Eley testified. "But when he pulled off the boards, we recognized it was a pretty obvious burn area."

The two investigated the boards, five thick pieces of plyboard that had been placed on top of the burn pit.

Eley said there were no signs that anything had been done to put out the smoldering debris underneath. When investigators removed the charred boards, white ash below remained pristine.

Eley noted a clear line of fire coming from the pit into the forest, with unburned material on both sides and charring on nearby trees. That shows the fire originated at the burn pit, he testified, and slowly crept out into the forest before engulfing the trees.

But defense attorney Kevin Fitzgerald pointed out in his cross-examination of Eley that investigators could not identify the exact start time of the fire.

Eley testified that it was inappropriate to speculate on the time it started, instead noting the time of the first 911 calls as the start of the fire.

Fitzgerald argued that it's an important factor to note, especially given the theory that the fire crept out from the burn pit.

He also pressed Eley on how he conducted his investigation, pointing out that he didn't follow certain recommendations outlined in the National Wildfire Coordinating Group guide to concluding fire origin, like taking field notes during the first day of his investigation.

His cross-examination of Eley will continue Friday.

'We managed them'

Assistant District Attorney Eric Senta played audio of one of the first phone conversations fire investigators had with Imig on June 16, two days after the fire started.

In the conversation, Imig is polite and cooperative. He confirms he was on the property the weekend of the fire, clearing branches and burning debris.

Investigators had not determined the cause of the fire and were not pressing Imig on his involvement in any crime. When they ask whether he had done any burning before the fire, Imig defends his actions.

"We had some burn piles," he tells investigators, "but we managed them."

In a later interview played for jurors, Eley asks Imig whether he thinks the fire crept out.

Imig tells him no.

"How can an ember float 40 feet?" he tells Eley.

Eley reminds him that fires can creep out from the ground, igniting small ground fuels along the way. Imig tells Eley that he had cleared the area and that there was no way the fire could have spread into the forest. Eley disagrees, saying the pit was in close contact with the nearby brushy forest, with no visible fire breaks.

"I don't think it went under the ground," Imig replies. "The fact that we saw it so high, I don't know what it means."

DeWitt also spoke with investigators. In interviews played for the jury Thursday she says she watched the burn pit the evening before the fire started and that it wasn't burning after dinner.

The next morning she placed the boards over the top of the pile. She tells investigators she thought the thick boards would be "hard to start" and would indicate whether the fire had reignited.

She tells investigators her plan was to check on them before she left. If the fire was still smoldering when they got ready to leave, she would know to extinguish it.

But later that day, while watering lilacs in the yard, she saw a fire emerge in the trees. She called 911 and quickly left the property with Imig and her 17-year-old son. She didn't have a chance to check the boards.